1. Field of the Invention
The present invention relates to electrical lead bonding, more particularly to the method and apparatus for bonding outer leads of a display panel to metal leads on bonding tape.
2. Description of the Prior Art
Tape automated bonding of semiconductor lead bonding to a supporting circuit board is well known. In this application the leads on the semiconductor device and the bonding tape are opaque and can be clearly seen by suitable apparatus when viewed from above the device. However, liquid crystal display (LCD) panels utilize transparent leads, such as tin oxide or the like, which are more difficult to see for alignment.
FIG. 1 shows a typical apparatus for bonding tape leads to LCD panel displays wherein alignment is very difficult. There are two kinds of light sources under the bonding stage 10. One is coaxial light from the charge coupled device (CCD) cameras 22 and the other is a normal light source 15. The coaxial light source in the CCD camera 22 is designed to see the indium tin oxide (ITO) alignment mark on the LCD panel 12. The normal light sources 15 on both sides of the CCD cameras 22 are designed to see the copper alignment mark on the polyimide tape carrier. The process flow of the outer lead bonding (OLB) operations on this conventional bonder is as follows. After temporary bonding of anisotropic conductive film (ACF), the back-paper film on the ACF is removed. The next step is alignment of the ITO pattern and the copper lead pattern. The coaxial light can see the square alignment marks of LCD panel on the monitor and the auto-alignment system will mark the positions. The coaxial light then is turned off and the normal light turned on. The alignment marks on the copper lead pattern then show up and auto-alignment system checks the position of marks differences and then makes an adjustment. When the differences are under control, the bonding step is performed. The process concept is good, but in the execution there are problems because of the opaqueness of the leads as described above.